PALEONTOLOGY AND THE PHENOTYPE

The ability to document changes in phenotype through time and space is one of the unique contributions that paleontology provides to evolutionary biology. The degree to which variation among the phenotypes of individual organisms represents genetic variation among true biological populations can not be address directly by the field of paleontology. This question is, however, central to every (paleo)biological study or application that is based on the recognition of species (identification or classification). The phenotype of an individual organism is a function of 1) its genetic composition, 2) the environment in which it lives and 3) the interaction between these factors. Population geneticists have recognized that genotypic contributions are a function nonheritable and heritable sources, which additionally can be transmitted as dominant or recessive alleles. Although considerable effort has been invested in the study of environmental influences on the phenotype (ecophenotypic variation), the relative importance of different scales of spatial and short term temporal variation have been under appreciated in paleontological applications. The third component, "interaction" of environment and genetics is a result of conspecific individuals responding independently (differently) to the same environmental stimulus based on small differences in their genotypes. If this interaction of genotype and environment (norm of reaction) is of significant magnitude, a researcher can not determine the significance of either genetic (evolutionary) or environmental variation, based on morphology alone. Approaches to the question of the correlation of morphology and genetics include: 1) comparison of hard part morphology vs. molecules of living forms; 2) application of paleontological morphometric methods to known modern environments; 3) careful comparison of morphology and changing environments through tightly constrained geologic time. The influence of hierarchical environmental variation on the skeletal phenotype of the modern bryozoan Electra pilosa will be used as an example for this presentation.